John,
It is truly amazing I was just begining to develop a serious interest
in birding around 1989 in Eugene where I lived at that time when one
summer nearly 1000 Vauks and Black swifts would swirl into a
abandoned church chimney. It was a sight that is truly hard to
explain, about as fascinating as 300 marbled godwits circling around
a jetty during migration. Just another wonder of birds.
-Scott Downes